The following steps give an example on how to
calculate the internal resistance of the super capacitor with the system MCU :
- Set SOH discharge current to 0A
(Register 0x09: SOH_SET1, SOH_I bits).
- Set AVI pin ratio to the backup
battery voltage as 1/4 (Register 0x0A: SOH_SET2, SOH_V_RATIO bits).
- Set AVI pin ratio to the
discharge current as 4 (Register 0x0A: SOH_SET2, SOH_I_RATIO bits).
- Select AVI pin output as battery
voltage (Register 0x0A: SOH_SET2, SOH_AVI_EN bits).
- Enable SOH function (Register
0x0B: CONTROL_STATUS, CHGR_SOH_EN bits).
- Wait for approximately 1ms for
AVI output voltage to stabilize.
- Read the backup battery voltage
at AVI pin with the MCU ADC (VBUB1).
- Set SOH discharge current to
200mA (Register 0x09: SOH_SET1, SOH_I bits).
- Discharge for 500ms (depending on
super capacitor characteristic, ask the capacitor vendor for
recommendation).
- Read the backup battery voltage
at AVI pin with the MCU ADC (VBUB2).
- Select AVI pin output as
discharge current (Register 0x0A: SOH_SET2, SOH_AVI_EN bits).
- Wait for approximately 1ms for
AVI output voltage to stabilize.
- Read the discharge current at AVI
pin with the MCU ADC (IBUB2).
- Set SOH discharge current to 0A
(Register 0x09: SOH_SET1, SOH_I bits).
Use the following equation for the system MCU to
calculate the internal impedance of the super capacitor and detect the capacitor
state of health.
Equation 7.